<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        *{margin:0;padding:0;}
        ul{list-style:none;}
        #box {
            height: 70px;
            width: 360px;
            padding-top: 360px;
            border:1px solid #ccc;
            margin:100px auto;
            overflow: hidden;
            background: url(images/01big.jpg) no-repeat;
        }
        #box ul{
            overflow: hidden;
            border-top:1px solid #ccc;
        }
        #box li {
            float: left;
            cursor:pointer;
        }
    </style>
    <script type="text/javascript">
        window.onload = function(){
            var boxs = document.getElementById("box")
            function fn(lis,bg){
                var lis = document.getElementById(lis);
                lis.onmouseover= function(){
                    boxs.style.background=bg
                }
            }
            fn("li1","url(images/01big.jpg) no-repeat")
            fn("li2","url(images/02big.jpg) no-repeat")
        } 
    </script>
</head>
<body>
<div id="box">
    <ul>
        <li id="li1"><img src="images/01.jpg" alt=""/></li>
        <li id="li2"><img src="images/02.jpg" alt=""/></li>
        <li id="li3"><img src="images/03.jpg" alt=""/></li>
        <li id="li4"><img src="images/04.jpg" alt=""/></li>
        <li id="li5"><img src="images/05.jpg" alt=""/></li>
    </ul>
</div>
</body>
</html>